Power supply that maintains auxiliary bias within target range

ABSTRACT

A power supply includes a switch configured to control flow of current output from an inductor to an output of the power supply. The switch receives a switching signal from a control circuit. An auxiliary bias is generated to power the control circuit. A bias circuit outputs a bias signal that is used to generate the auxiliary bias. The bias circuit senses a level of the auxiliary bias to control output of the bias signal. Output of the bias signal may be controlled to maintain the level of the auxiliary bias at a target level or within a target range.

TECHNICAL FIELD

The present disclosure relates generally to power supplies, and moreparticularly to maintaining an auxiliary bias of a power supply within atarget range.

BACKGROUND

Power supplies may be used in electronic applications to convert aninput voltage to a desired output voltage to power one or moreelectronic devices. Some power supplies may be classified as either alinear power supplies or a switch-mode power supply (SMPS). Switch-modepower supplies may be configured to operate more efficiently than linearpower supplies. A switched-mode power supply may include a switch that,when switching on and off, stores energy in an inductor and dischargesthe stored energy to an output of the switched mode power supply. Theswitch may be controlled by a controller, which outputs switchingsignals to turn the switch on and off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an example switch-mode power supply.

FIG. 2 shows a schematic diagram of an alternative example switch-modepower supply, illustrating an example cascode version of the switch-modepower supply shown in FIG. 1.

FIG. 2A shows a schematic diagram of a second alternative exampleswitch-mode power supply, illustrating another example cascode versionof the switch-mode power supply shown in FIG. 1.

FIG. 3 shows a schematic diagram of a third alternative exampleswitch-mode power supply.

FIG. 4 shows a schematic diagram of a fourth alternative exampleswitch-mode power supply, illustrating an example cascode version of theswitch-mode power supply shown in FIG. 3.

FIG. 5 shows a schematic diagram of a fifth alternative exampleswitch-mode power supply, illustrating another alternative examplecascode version of the switch-mode power supply shown in FIG. 3.

FIG. 6 shows a schematic diagram of a sixth alternative exampleswitch-mode power supply.

FIG. 7 shows an example processing system that may be implemented as oneor more components of a switch-mode power supply.

FIG. 8 shows a flow diagram of an example method of operating a powersupply to maintain an auxiliary bias within a target range.

FIG. 9 shows a flow diagram of an alternative method of operating apower supply to maintain an auxiliary bias within a target range.

FIG. 10 shows a flow diagram of another alternative method of operatinga power supply to maintain an auxiliary bias within a target range.

DETAILED DESCRIPTION

The present disclosure describes a switch-mode power supply thatincludes a control circuit configured to control switching of switchingcircuitry, and a bias circuit configured to supply power to the controlcircuit. The bias circuit may output a bias signal that powers thecontrol circuit. The bias circuit may generate and/or output the biassignal independent of a switching signal that is output from the controlcircuit to control switching of the switching circuitry. The biascircuit may be configured to operate in a hysteretic manner to generateand/or output the bias signal. The bias circuit may include a biascontroller that is configured to sense a level of the bias being appliedto the control circuit. Based on the level that is sensed, the biascontroller may be configured to determine whether to adjust one or moreoutput signals that may be used to control the level of the bias.

Switch-mode power supplies may be used in various applications, such aslighting applications. For example, switch-mode power supplied may beused to power a light source, such as one or more light-emitting diodes(LEDs). The LEDs may be connected to an output of the switch-mode powersupply and/or may be configured as an output load of the switch-modepower supply. In addition, the LEDs may be powered by a direct current(dc) signal having a dc voltage. In one example, the dc voltage may beapproximately 200 volts, although other voltages may be used to powerthe LEDs. In some example configurations, the switch-mode power supplymay include and/or be connected to a rectifier that converts analternating current (ac) signal to a rectified ac signal. As an example,the rectifier may receive a 120 volt ac signal, such as from a walloutlet, and convert the 120 volt ac signal to a rectified 120 volt acsignal. The switch-mode power supply may then convert the ac rectifiedsignal to a dc signal, such as a 200 volt dc signal, to power the LEDs.

FIGS. 1-6 show various example configurations of switch-mode powersupplies. The switch-mode power supplies shown in FIGS. 1-6 are shown asboost converters, although similar configurations may be used in othertypes of switch-mode power supplies, such as buck or flyback converters,and/or may be used in power supplies that are configured to performac-dc, dc-ac, and/or ac-ac conversion.

FIG. 1 shows a schematic diagram of an example switch-mode power supply100. The example switch-mode power supply 100, switching circuitrycomprising a switch M1. The switch M1 may be an electronic component ordevice that switches between an “on” state and an “off” state. In oneexample, the switch M1 may be an electronic component or device thatswitches between being completely “on” and completely “off.” The switchM1 may be a metal-oxide-semiconductor field-effect transistor (MOSFET),although other types of switches may be used.

The switch M1 may be in communication with and/or connected to aninductor L1. Where the switch M1 is a MOSFET, a drain of the MOSFET M1may be connected to the inductor L1. The inductor L1 may be connected tothe switch M1, and may also be connected to and/or in communication withan input voltage source Vin. The input voltage source may be a constantdirect current (dc) source or a rectified alternating current (ac)source. In some configurations, the input voltage source Vin may be acomponent of the switch-mode power supply 100. In other exampleconfigurations, the input voltage source Vin may be a component that isseparate from and/or external to the switch-mode power supply 100 andthat supplies the dc or rectified ac signal to the switch-mode powersupply 100. The example switch mode power supply 100 may further includea diode D1 that is connected to and/or in communication with the switchM1. Where the switch M1 is a MOSFET, the diode D1 may be connected tothe drain of the MOSFET. The diode may be configured to be in an “on”state or an “off” state. The diode D1 may be also be connected to and/orin communication with an output of the switch-mode power supply 100.When the diode is “on,” current output from the inductor L1 may passthrough the diode D1 to the output. Alternatively, when the diode is“off,” current output from the inductor L1 may not pass through thediode D1 to the output.

The output of the switch-mode power supply 100 may include an outputcapacitor C1 connected in parallel with an output load Z1. The outputload Z1 may include one or more electronic devices and/or componentsconnected in series, in parallel, or a combination thereof. The outputload Z1 may be configured to draw current, and an output voltage Voutmay be generated across the output load Z1. The output load may includeone or more resistors, capacitors, inductors, diodes, transistors, orother types of active or passive components. In some exampleconfigurations, the output load Z1 may be configured to perform apredetermined function, such as output light. For example, the outputload Z1 may include one or more LEDs, such as high brightness LEDs. Theoutput load Z1 and/or the switch-mode power supply 100 may be part of alighting system, such as a downlight, spot light, light bulk, lamp,light fixture, sign, retail display, transportation, lighting foremergency vehicles, or portable lighting system, as examples. In someexample configurations, an output voltage of 200 dc volts may begenerated across the output load Z1 and/or across the output of theswitch-mode power supply 100, although other voltages may be generated.Other configurations of the output load Z1 are possible. The output loadZ1 may or may not be included on the same circuit board or in the samepackage as the components of the switch-mode power supply 100.

During operation of the example switch-mode power supply 100, when theswitch M1 is turned “on,” electrical current output from the inductor L1may pass through the switch M1 to ground. Also, when the switch M1 is“on,” the inductor L1 may be charged by the input voltage source Vin.Further, when the switch M1 is “on,” a voltage across the switch (e.g.,a drain-source voltage) may be approximately zero volts, which mayreverse bias the diode D1, causing no current or substantially nocurrent to pass through the diode D1 to the output. Alternatively, whenthe switch M1 is “off,” no current passes through the switch M1. Also,when the switch M1 is turned “off,” a voltage (e.g., the drain-sourcevoltage) across the switch M1 may be at a level that forward biases thediode D1, causing current output from the inductor to pass through thediode D1 to the output of the switch-mode power supply 100.

The switch-mode power supply 100 may further include a control circuit110 that is configured to control switching of the switch M1. Thecontrol circuit 110 may control switching of the switch M1 by generatingand/or outputting switching signals that switch the switch M1 “on” and“off. ” The switching signal output from the control circuit 110 mayalso determine a time duration that the switch M1 is “on.” The switchingsignal may be of any type that can turn the switch M1 “on” and “off.”For example, the switching signal may be a direct current (dc) signalthat has at least two levels, including a first dc level that turns theswitch M1 “on” and a second dc level that turns the switch M1 “off.”Alternatively, the switching signal may be a pulse-width modulated (PWM)signal. Each of the PWM signals may have an associated amplitude,frequency, period, and/or duty cycle. The control circuit 110 may beconfigured to determine the amplitude, frequency, period, and/or dutycycle for each of the PWM signals. In some configurations, the controlcircuit 110 may be configured to determine to maintain the amplitude,frequency, period, and/or duty cycle the same between two or moreswitching signals and/or may be configured to determine to change theamplitude, frequency, period, and/or duty cycle between two or moreswitching signals.

The control circuit 110 may be configured to output the switchingsignals from an output GD1 to an input of the switch M1. Where theswitch M1 is a MOSFET, the switching signals may be output to a gateterminal of the MOSFET. When a voltage of the switching signal appliedto the gate generates a gate-to-source voltage that exceeds a thresholdvoltage, the switch M1 may be turned “on.” When the voltage applied tothe gate generates a gate-to-source voltage that is below the thresholdvoltage, the switch may be turned “off.”

The control circuit 110 may further include a voltage bias inputterminal Vcc. The voltage bias input terminal Vcc may be configured toreceive a bias signal, such as a bias voltage Vbias that is used topower the control circuit 110. the bias may be referred to as anauxiliary bias or a housekeeping bias. The bias voltage Vbias may be apredetermined amount determined and/or required by the control circuit110. In one example, the voltage required to power the control circuit110 may be of an order much less than the input voltage Vin. Forexample, the voltage Vbias may be in a range of one-twentieth toone-fifth of the input voltage Vin.

The switch-mode power supply 100 may further include a bias circuit 120that is configured to output a bias signal that is used to power thecontrol circuit 110. The bias signal may generate a bias voltage Vbiasthat is applied to the voltage bias input terminal Vcc. The bias circuit120 may include a switch M3 that is in connection with a diode D2. Theswitch M3 may also be connected to the voltage bias input terminal Vccof the control circuit 110, for example at node B shown in FIG. 1. Thediode D2 may be connected to the switch M3 and may also be connected tothe switch M1, for example at node A shown in FIG. 1. Where the switchM1 is a MOSFET, the diode D2 may be connected to the drain of the MOSFETM1.

The switch M3 may be configured to switch between an “on” state and an“off” state. The diode D2 may also be configured to switch between an“on” state and an “off” state. When both the diode D2 and the switch M3are “on,” current may flow through the diode D2 and the switch M3, fromnode A to node B. The charge flowing from the switch M3 to the node Bmay be stored in energy storing circuit C2. The energy storing circuitC2 may be connected to the voltage bias input terminal Vcc, and may beconfigured to generate and/or maintain the voltage bias Vbias that isapplied to the voltage bias input terminal Vcc. The energy storingcircuitry C2 may be a capacitor, although other types of energy storingcircuitry may be used. The energy storing circuitry C2 may be or mayinclude one or more circuit elements, such as one or more capacitors,inductors, resistors, diodes, transistors, batteries, other circuitelements, or any combination thereof, that is capable of storing anddischarging energy.

The bias circuit 120 may further include a bias controller 130 that isconfigured to control switching of the switch M3. The bias circuit mayinclude an output terminal GD2 that is configured to output one or moreswitching signals that turn the switch M3 “on” and “off.” The outputterminal GD2 may be in communication with an input terminal of theswitch M3. Where the switch M3 is a MOSFET, the input terminal may be agate of the MOSFET M3. The switching signals applied to the gate M3 maybe any type that is configured to turn the switch “on” and “off,” suchas dc signals or PWM signals. In some example configurations where theswitching signals are PWM signals, the bias controller 130 may beconfigured to change or adjust an associated amplitude, frequency,period, and/or duty cycle between two or more PWM signals in order tocontrol switch M3. In alternative configurations where the switchingsignals are dc signals, the controller 130 may be configured to output adc signal at or above a threshold level or value that turns the switchM3 “on.” The controller 130 may also be configured to output a dc signalbelow the threshold level or may cease outputting a dc signal at orabove the threshold level to turn the switch M3 from “on” to “off.”Various configurations and/or types of switching signals to controlswitching of the switch M3 are possible.

The bias controller may further include an input terminal SNS1 that isconfigured to receive and/or sense the bias voltage Vbias at node B. Inresponse to sensing the bias voltage Vbias at node B, the biascontroller 130 may be configured to determine whether the bias voltageVbias is at a target level and/or within a target range. The targetlevel may be within the target range. Additionally, the target range mayhave and/or be defined by an upper level and a lower level.

The bias controller 130 may be configured to determine whether the biasvoltage Vbias sensed at the input terminal SNS1 is too high. The biascontroller 130 may determine that the voltage bias Vbias is too highwhen the sensed voltage bias is at a level that is greater than a biasvoltage needed to power the control circuit 110, greater than apredetermined threshold voltage, greater than the target level, and/orgreater than the upper bound of the target range. Also, the biascontroller 130 may be configured to determine whether the bias voltageVbias is too low. The bias controller 130 may be configured to determinethat the bias voltage Vbias is too low when the sensed bias voltageVbias is at a level that is less than a bias voltage needed to power thecontrol circuit 110, less than a predetermined threshold voltage, lessthan the target level, and/or less than a lower bound of the targetrange.

The bias controller 130 may be configured to control switching of theswitch M3 in response to sensing the bias voltage Vbias. Based on thebias voltage Vbias that is sensed at the input terminal SNS1, the biascontroller 130 may be configured to determine whether to output aswitching signal, to cease outputting a switching signal, and/or toadjust one or more characteristics of the switching signal being outputto the switch M3. For example, if the bias voltage Vbias is too high,then the bias controller 130 may be configured to turn the switch M3“off,” such as by ceasing output of the switching signal. Alternatively,the bias controller 130 may be configured to reduce a duty cycle of aPWM signal that is being applied to the switch M3, which may reduce anamount of time that the switch M3 is “on” during a period of the PWMsignal. By turning the switch M3 “off” and/or reducing the amount oftime that the switch M3 is “on” during PWM cycles, no current or areduced amount of current may flow through the switch M3, which mayeliminate and/or reduce the amount of charge being stored in the energystoring circuit C2. In turn, the bias voltage Vbias at node B maydecrease to a desirable level, such as to a target level and/or within atarget range.

Similarly, if the bias voltage Vbias is too low, then the biascontroller 130 may be configured turn the switch M3 “on,” such as byoutputting the switching signal to the switch M3. Alternatively, thebias controller 130 may be configured to increase a duty cycle of a PWMsignal that is being applied to the switch M3, which may increase anamount of time that the switch M3 is “on” during a period of the PWMsignal. By turning the switch M3 “on” and/or increasing the amount oftime that the switch M3 is “on” during PWM cycles, current or anincreased amount of current may flow through the switch M3, which mayincrease the amount of charge being stored in the energy storingcircuitry C2. In turn, the bias voltage Vbias at node B may increase toa desirable level, such as to the target level and/or within the targetrange.

The output terminal GD2, the switch M3, the bias voltage Vbias at nodeB, and the input terminal SNS1 may form a feedback loop in theswitch-mode power supply 100. Using the feedback loop, the biascontroller 130 may output a switching signal at the output terminal GD2,which may generate a bias voltage Vbias that is fed back to the biascontroller 130. The bias controller may compare the sensed bias voltageVbias that is fed back with the target level or target range anddetermine whether to adjust the output of the output terminal GD2.

In more detail, the bias controller 130 may output a switching signal tothe switch M3, causing the switch M3 to turn “on.” By turning “on,”current may flow through the switch M3 to node B, causing a bras voltageVbias to be generated at node B. The level of the bias voltage Vbias maybe sensed at the input terminal SNS1, and based on the level that issensed, the bias controller 130 may determine whether to maintainapplication of the switching signal cease application of the switchingsignal, and/or adjust one or more characteristics of the switchingsignal in order to maintain the voltage Vbias at or within a targetlevel or target range, or to adjust the voltage Vbias to be at or withina target level or target range.

When current is not flowing through the switch M3 (e.g, because theswitch M3 and/or the diode D2 is “off”), the bias voltage Vbias at nodeB may decrease because charge stored in energy storing circuit C2 may bedischarged into a load Z2 that is connected to the energy storingcircuit C2. In one example, the load Z2 may be connected in parallelwith the energy storing circuit C2. The load Z2 may function as acurrent sink. Charge that may be stored in the energy storing circuit C2may be discharged and supplied to the load Z2. Additionally, some chargestored in the capacitor C2 may also be discharged into the voltage biasinput terminal Vcc of the control circuit 110. Without the load Z2,charge may only be discharged into the voltage bias input terminal Vcc,and which may prevent the bias voltage Vbias from decreasing from avoltage level that is too high to the target level or a level that iswithin the target range.

The load Z2 may include one or more electronic devices that areconfigured to draw current and/or function as a current sink. Asnon-limiting examples, the load Z2 may include one or more active and/orpassive electronic devices, such as resistors, capacitors, inductors,diodes, transistors, or combinations thereof. In addition, the load Z2may include one or more light-emitting diodes (LEDs), one or morecooling systems, one or more zener diodes, or any combination thereof.The components of the load Z2 may be connected in series, in parallel,or a combination thereof. The load Z2 may include one or more packagedcomponents. The load may provide a function in addition to and/or otherthan generating a voltage Vbias at the voltage bias input terminal Vcc.For example, the load may actively control optical and/or thermalcharacteristics of a lighting device and/or a lighting system. Opticaland/or thermal characteristics may include color, brightness, and/ortemperature, as examples. Alternatively or in addition, the load mayprovide optical and/or thermal energy to the lighting device and/or thelighting system. FIG. 1 shows the load Z2 being a component of theswitch-mode power supply 100 that is external to the control circuit110. In other configurations, the load Z2 may be an electronic componentof the control circuit 110. Various configurations are possible.

During operation of the switch-mode power supply 100, the input voltagesource Vin may output and/or supply a dc input signal or a rectified acinput signal. In some examples, a voltage of level of the dc orrectified ac signal may be 120 volts rms, although other voltages may beprovided by the input voltage source Vin. At startup of the switch-modepower supply 100, the input signal may pass through a startup resistorR1 and applied to the voltage bias input terminal Vcc, which may powerthe control circuit 110. The resistor R1 may be configured to supply theappropriate current so that Vcc voltage is raised to the target leveland/or within the target range at which the control circuit isconfigured to operate.

When the control circuit 110 is powered “on,” the control signal may beconfigured to output a switching signal from the output terminal GD1 tothe switch M1. Upon receipt of the switching signal, the switch M1 mayturn “on.” When the switch M1 turns “on,” current may flow from theinductor L1 through the switch M1 to ground. When current flows throughthe switch M1, a voltage across the switch M1 (e.g., the drain-sourcevoltage across the switch M1) may be zero volts or substantially zerovolts. When the voltage across the switch M1 is zero volts, the diode D2may be reverse biased, and current may not from flow from node A throughthe diode D2.

The switching signal may also turn the switch M1 “off.” When the switchM1 turns “off,” the voltage across the switch (e.g., the drain-sourcevoltage) may increase. The voltage across the switch M1 may increase toa predetermined threshold level at node A, which may forward bias theD2, turning the diode D2 “on.” The input terminal SNS2 may be configuredto sense the voltage at node A (e.g., the drain voltage of the switchM1), and may sense when the voltage at node A reaches the thresholdlevel. By sensing the voltage at node A, the bias controller 130 may beconfigured to turn the switch M3 “on,” if the switch M3 is not alreadyin the “on” state. When both the diode D2 and the switch M3 are “on,”current at node A may pass through the diode D2 and the switch M3 tonode B. As previously described, the energy storing circuit C2 may storethe charge received at node B, generating a bias voltage Vbias at nodeB. As current is supplied from the switch M2 and charge is stored by theenergy storing circuit C2, the voltage across the energy storing circuitC2 may increase, thereby increasing the bias voltage Vbias being appliedto the voltage bias input terminal Vcc.

The input terminal SNS1 of the bias controller 130 may sense the biasvoltage Vbias being applied to the voltage bias input terminal Vcc. Thebias controller 130 may be configured to know the target level or targetrange at which the control circuit 110 is configured to operate and/orat which the bias voltage Vbias is to be maintained. The bias controller130 may compare the bias voltage Vbias at node B with the target levelor target range to determine whether the bias voltage Vbias is at thetarget level or within the target range. If the bias voltage Vbias is atthe target level or within the target range, then the bias controller130 may be configured to maintain application of the switching signal onthe switch M3 and/or to not adjust any characteristics of the switchingsignal being output to the switch M3.

Alternatively, if the sensed bias voltage Vbias is not at the targetlevel or is outside of the target range, then the bias controller 130may be configured to change the switching signal that is being appliedto the switch M3. Where the bias voltage Vbias is too high, the biascontroller 130 may be configured to turn “off” the switch M3 and/orreduce the amount of time in between switching cycles that the switch M3is “on” in order to reduce the voltage bias Vbias. For example, wherethe switching signal is a dc signal, the bias controller 130 may beconfigured to cease output of the dc signal or may be configured tooutput the dc signal at a level that is less than a threshold level thatturns the switch M3 “on.” Alternatively, where the switching signal is aPWM signal, the bias controller 130 may be configured to decrease theduty cycle of the switching signal.

After turning “off” the switch M3 and/or reducing the amount of timethat the switch M3 is “on” during switching cycles, the bias voltageVbias may decrease to a level that is at the target level and/or iswithin the target range. In some situations, the voltage bias Vbias maydecrease to a level that is too low, such as below the target level orbelow a lower bound of the target range. The input terminal SNS1 maysense that the bias voltage Vbias has decreased too low. In response,the bias controller 130 may be configured to change the switchingsignal. For example, where the switching signal is a dc signal, the biascontroller 130 may be configured to output the dc signal at a level thatis at or above a threshold level that turns the switch M3 “on.”Alternatively, where the switching signal is a PWM signal, the biascontroller may be configured to increase the duty cycle of the PWMsignal to increase the amount of time that the switch M3 is “on” duringswitching cycles.

The bias controller 130 may continually sense the bias voltage Vbias atnode B and adjust the switching signal applied to the switch M3 based onthe sensed voltage so that the bias voltage Vbias is maintained at atarget level and/or within a target range. In this way, the bias circuit120 may be configured to supply a bias signal to power the controlcircuit 110 in a hysteretic manner. As the bias voltage Vbias increasesto an upper bound of a target range, the bias controller 130 may adjustthe switching signal applied to the switch M3 to decrease the biasvoltage Vbias. Also, as the bias voltage Vbias decreases to a lowerbound of a target range, the bias controller 130 may adjust theswitching signal applied to the switch M3 to increase the bias voltageVbias.

Additionally, the bias circuit 120 may be configured to control the biasvoltage Vbias applied to the control circuit 110 independent of theswitching signals output from GD1 that are being applied to the switchM1. Rather than monitor the switching signal output from GD1 and/or anoutput Vout of the switched-mode power supply 100 and adjusting theswitching signal applied to the switch M3 based on the output from GD1and/or the output Vout of the switch-mode power supply 100, the biascircuit 120 may monitor the bias voltage Vbias itself, and determinewhether to adjust the switching signals applied to the switch M3 basedon the level of the bias voltage Vbias.

Additionally, the bias circuit 120 and/or the bias controller 130 may beconfigured to set and/or determine a maximum limit on the amount of timethat the switch M3 may be “on.” in some example configurations, themaximum limit may be a predetermined value. The maximum limit mayprevent saturation by enabling the bias circuit 120 and/or the biascontroller 130 to know the amount of increase in the inductor current.In some example embodiments, the bias circuit 120 and/or the biascontroller 130 may be capable of monitoring the current passing throughM3 by sensing the voltage across R3 (e.g., by sensing a voltagedifference between the SNS1 and the CS1 input terminals). By sensing thevoltage across R3, the bias controller 130 may be configured to takeprotective action if the current exceeds a predetermined thresholdvalue.

FIG. 2 shows a schematic diagram of an example switch-mode power supply200, illustrating an example cascode configuration of the exampleswitch-mode power supply 100, shown in FIG. 1. In the exampleswitch-mode power supply 200, the switching circuitry may include twoswitches, a first switch M1 and a second switch M2, that are configuredin a cascode configuration. One advantage of the cascode configurationmay be that the switch M1 and a switch M3 in a bias circuit 220 may bothbe MOSFETs, may be rated for a low voltage, and/or may have a small sizefor easy integration with a bias controller 230 as an integratedcircuit. Additionally, the second switch M2 may be rated for a highvoltage that may be equal to or higher than the output voltage. Thefirst switch M1 of the example switch-mode power supply 200 may be incommunication with a control circuit 210, which outputs switchingsignals via an output terminal GD1 to turn the first switch M1 “on” or“off.” The example switch-mode power supply 200 may further include asecond switch M2 that is connected to the first switch M2. The firstswitch M1 and the second switch M2 may be connected to a diode D2 of abias circuit 220. Where the first switch M1 and the second switch M2 areboth MOSFETs, a drain of the first switch M1 may be connected to thediode D2, and a source of the second switch M2 may be connected to thedrain of the first switch M1 and the diode D2.

The example switch-mode power supply 200 may further include a startupresistor R1. The startup resistor R1 may also be connected to an inputterminal (e.g., a gate) of the switch M2, for example at node C. Thestartup resistor R1 may also be connected at node C to a capacitor C3connected in parallel with a zener diode D3. In one exampleconfiguration, the capacitor C3 may have a small capacitance and/or maybe configured to charge relatively quickly, which may provide theexample switch-mode power supply 200 with fast startup capabilities.

During a startup operation of the switch-mode power supply 200, thevoltage at node C may rise from zero volts and may be clamped to avoltage of the zener diode D3. As the voltage at node C rises, the biascontroller 230 may sense the voltage of node C at input terminal G2 andturn on M3 by sending a switching signal from the output terminal GD2.Also, during startup, the voltage at node B may initially be zero volts.When the third switch M3 is turned “on,” the capacitor C2 may be chargedby current passing through the inductor L1, the second switch M2, thediode D2, and the third switch M3. As the capacitor C2 is being charged,the voltage across the capacitor C2 (i.e., the voltage at node B) mayrise to the voltage at node C that is clamped by the zener diode D3 lessthe threshold voltages of the second switch M2, the third switch M3, andthe voltage drop across the diode D2.

During steady-state operation of the switch-mode power supply 200, thefirst switch M1 may be configured to be turned “on” by receiving aswitching signal from an output terminal GD1 of the control circuit 110.When the first switch M1 is turned “on,” the second switch M2 may alsoturn “on,” and current output from the inductor L1 may pass through thesecond switch M2 and the first switch M1 to ground. Subsequently, thefirst switch M1 may be turned “off.” Also, at this time, the secondswitch M2 may remain “on.” Because the first switch M1 is turned “off,”voltage across the first switch M1 (e.g., drain-source voltage acrossthe first switch M1) may increase from a level of zero volts when thefirst switch M1 was “on.” The voltage across the first switch M1 mayincrease to a threshold voltage level that forward biases the diode D2.An input terminal SNS2 of the bias controller 230 may sense that thevoltage at node A is at the threshold voltage level and the biascontroller 230 may output a switching signal to turn the switch M3 “on,”provided that the switch M3 is not already “on.” Because the secondswitch M2 is “on,” current may flow from the inductor L1 through thesecond switch M2, the diode D2 and the switch M3 of the bias circuit230, to node B, whose a bias voltage Vbias is generated and applied to abias voltage input terminal Vcc of the control circuit 210.

The bias controller 230 may be configured to control switching of theswitch M3 by outputting switching signals from an output terminal GD2 toan input terminal (e.g., a gate) of the switch M3, as previouslydescribed. The switch-mode power supply 200 may be configured so thatthe second switch M2 turns “off” when the switch M3 is turned “off.” Insome example configurations, to ensure that the second switch M2 is“off,” an input terminal (e.g., the gate) of the second switch M2 atnode C may be connected to an input terminal SHRT of the control circuit210 via a connection 240. The control circuit 210 at the input terminalSHRT may be configured to reduce the voltage level of the input terminalof the second switch M2, which may ensure that a voltage lower than athreshold voltage of the second switch M2 is applied between thegate-source terminals of the second switch M2 and that the second switchM2 is completely “off.” When the second switch M2 is “off,” voltage atnode D (e.g., the drain of the second switch) may increase, and forwardbias the diode D1 so that current output from the inductor L1 is sent tothe output of the switch-mode power supply 200.

FIG. 2A shows a schematic diagram of an alternative example switch-modepower supply 200A. The example switch-mode power supply 200A may besimilar to the example switch-mode power supply 200 shown in FIG. 2. Onedifference between the switch-mode power supply 200A and the switch-modepower supply 200 is that there a bias circuit 210A may not include thethird switch M3 and a control circuit 210A may not have a terminal SHRTconnected to an input terminal of a second switch M2. Rather, a diode D2is connected to both node A and node B.

During startup of the example switch-mode power supply 200A, voltages atnodes B and C may initially be zero. Current through a startup resistorR1 may charge a capacitor C3, which may cause the voltage across thecapacitor C3 (i.e., the voltage at node C) to rise. As the voltage atnode C rises beyond the gate-source threshold of the second switch M2,the second switch M2 may turn “on.” The voltage at node C may continueto rise to a threshold level that causes the diode D2 to be forwardbiased. When the second switch M2 is “on” and the diode D2 is forwardbiased, current discharged from the boost inductor L2 may start flowthrough the second switch M2 and the diode D2 to node B, which mayincrease the voltage at node B. Current discharged from the boostinductor L1 may continue to flow through the second switch M2 and thediode D2 until the zener diode D3 clamps a voltage at node C to thepredetermined zener voltage of the zener diode D3. The voltage at nodeB, which is the bias voltage Vbias applied to the input terminal Vcc ofthe control circuit 210A, may reach a level equal to the voltage at nodeC less the threshold voltage of the third switch M3 and the voltage dropacross the diode D2.

During steady-state operation of the example switch-mode power supply200A, the control circuit 210A may output a switching signal from theoutput terminal GD1 to the first switch M1 to turn the first switch M1“on.” When the control circuit 210A outputs a switching signal to turnthe first switch M1 “on,” the voltage at node A may be pulled to ground,which may cause the second switch M2 to be turned “on.” When the firstswitch M1 and the second switch M2 are both “on,” current dischargedfrom the inductor L1 may pass through the second switch M2 and the firstswitch M1 to ground. Also, when the first switch M1 and the secondswitch M2 are both “on,” the diode D2 may be reverse biased when thevoltage at node B is at the target level or within the target range ofthe voltage bias Vbias being applied to the input terminal Vcc.

Farther, during steady-state operation, the control circuit 210A mayoutput a switching signal at the output terminal GD1 to turn the switchM1 “off.” When the first switch M1 is turned “off,” the voltage at nodeA may rise from zero volts to a threshold voltage that causes the diodeD2 to be forward biased. When the second switch M2 is “on” and the diodeD2 is forward biased, current being discharged from the inductor L1 mayflow through the second switch M2 and the diode D2 to node B. The biascontroller 230A may determine that the diode D2 is forward biased bysensing the voltage at node A at the input terminal SNS2 and the voltageat node B at the input terminal SNS1. When the bias controller 230Asenses that the diode D2 is forward biased, the bias controller 230A,the bias controller 230A may also determine whether the voltage at nodeB measured at the input terminal SNS1 is at an or has exceeded an upperbound of a target range. If the voltage at node B is at or has exceedthe upper bound, then bias controller 230A may be configured to pull thevoltage at node C below a predetermined threshold value using a terminalG2 that is connected to the gate of the second switch M2 at node C. Thebias controller 230A may pull the voltage on node C below thepredetermined threshold value so that the second switch M2 is turned“off.” Alternatively, if the voltage at node B is before the upperbound, then the bias controller 230A may be configured to start oractivate a timer. The timer may be activated for a predetermined periodof time. In some example configurations, the predetermined period oftime may be about one one-hundredth of a time that the capacitor C2takes to charge from zero volts to the voltage bias Vbias. For example,if the capacitor C2 takes 100 microseconds to charge from zero volts tothe voltage bias Vbias, then the predetermined period of time may be onemicrosecond. When the predetermined period of time elapses, the biascontroller 230A may pull the voltage on node C below the predeterminedthreshold value so that the second switch M2 is turned “off.” When thesecond switch M2 is turned “off,” current being discharged from theinductor L2 may pass through the diode D1 to the output of the exampleswitch-mode power supply 200A.

In some example configurations, the bias controller 230A may beconfigured to adjust TD2 based on a feedback loop to control voltage atnode B. The feedback loop may be a loop formed between the inputterminal SNS1 that senses the voltage at node B and the terminal G2.

Additionally, like the bias circuit 120 shown in FIG. 1, the biascircuit 220A may be configured to control the bias voltage Vbias appliedto the control circuit 210A independent of the switching signals outputfrom GD1. Rather than monitor the switching signal output from GD1and/or an output Vout of the example switch-mode power supply 200A anddetermine when to switch off the first switch M1 and the second switchM2, the bias controller 220A may monitor the bias voltage Vbias itself,and determine when to switch the first switch M1 and the second switchM2 “on” based on the level of the bias voltage Vbias.

FIG. 3 shows a schematic diagram of an alternative example switch-modepower supply 300. In the alternative example switch-mode power supply300, a control circuit 310 may be configured to alternatingly send aswitching signal to a switch M1 to turn the switch M1 “on” and “off” orto a switch M3 of a bias circuit 320 to turn the switch M3 “on” and“off.” In particular, the control, circuit 310 may include an outputterminal GD1 that is configured to output the switching signals to aninput 342 of a multiplexer 340. The multiplexer 340 may include multipleoutputs, including a first output 344 and a second output 346. The firstoutput 344 may be connected to an input (e.g., a gate) of the switch M1.The second output 346 may be connected to an input (e.g., a gate) of theswitch M3. The input 342 of the multiplexer 340 may be configured to bealternatingly connected to the first output 344 or the second output346. When the input 342 is connected to the first output 344, theswitching signal output from the output terminal GD1 of the controlcircuit 310 may be sent to the input of the switch M1 to turn the switchM1 “on” and “off.” Alternatingly, when the input 342 is connected to thesecond output 346, the switching signal output from the output theoutput terminal GD1 of the control circuit 310 may be sent to the inputof the switch M3 to turn the switch M3 “on” and “off.”

In operation, when the input 342 of the multiplexer 340 is connected tothe first output 344, one or more switching signals may be output fromthe output terminal GD1 to the input terminal of the switch M1 to turnthe switch M1 “on” and “off.” When the switch M1 is “on,” current outputfrom inductor L1 may pass through the switch M1 to ground. When theswitch M1 is “off,” current output from the inductor L1 may pass throughthe diode D1 and to the output of the switch-mode power supply 300.Also, when the control circuit 310 is switching the first switch M1 “on”and “off,” the switch M3 is “off,” and so current may not flow throughthe diode D2 and the switch M3, from node A to node B.

Alternatively, when the input 342 of the multiplexer 340 is connected tothe second output 346, one or more switching signals may be output fromthe output terminal GD1 to the input terminal of the switch M3 to turnthe switch M3 “on” and “off.” Because the input 342 of the multiplexer340 is connected to the second output 346 instead of the first output344, the switch M1 is “off” and the voltage across the switch M1 (e.g.,the drain-source voltage) may increase. When the voltage increases to athreshold level, the diode D2 may be forwarded biased and turn “on.”When the switching signal, output from the output terminal GD1 turns theswitch M3 “on,” current output from the inductor L1 may be sent throughthe diode D2 and the switch M3 of the bias circuit 320, to node B. Atnode B, charge from the current may be stored in the energy storingcircuit C2, and a bias voltage Vbias may be generated across the energystoring circuit C2 and applied to the voltage bias input terminal Vcc.When the switching signal output from the output terminal GD1 turns theswitch M3 “off,” current output from the inductor L1 may pass throughthe diode D1 and to the output of the switch-mode power supply 300.Also, when the control circuit 310 is switching M3 “on” and “off,” theswitch M1 is “off,” and so current may not flow through the switch M1 toground.

As previously described, when current continually flows from node Athrough the diode D2 and the switch M3 to node B, the bias voltage Vbiasgenerated at node B may increase as charge is stored in the energystoring circuit C2. Also, when no current is flowing to node B, the biasvoltage Vbias generated at node B may decrease as charge stored in theenergy storing circuit C2 may be discharged into the load Z2. The biascontroller 330 may be configured to determine and/or sense the biasvoltage Vbias at an input terminal SNS1. Additionally, the biascontroller 330 may be configured to operate in a hysteretic manner tocontrol the bias voltage Vbias so that the bias voltage Vbias is at atarget level and/or within a target range. In particular, the biascontroller 330 may determine a level of the bias voltage Vbias at theinput terminal SNS1, and in response to determining the level, the biascontroller may output a control signal at an output terminal MX1 to themultiplexer 340 mat configures the input terminal 342 to be eitherconnected to first output 344 or the second output 346.

To illustrate, the bias voltage Vbias may have an associated targetvalue that is within a target range having an upper bound and a lowerbound. In one example, the target value may be 12 volts, and an upperbound of a target range may be 13 volts, and a lower bound of a targetrange may be 11 volts, although other voltages may be used. In aninitial condition, the input 342 may be connected to either the firstoutput 344 or to the second output 346. If, for example, the input 342is connected to the first output 344, then no current may flow throughthe diode D2 and the switch M3 to node B, and the bias voltage Vbias maydecrease. The bias voltage Vbias may decrease to the lower bound of thetarget range. The bias controller 330 may sense at the input terminalSNS1 that the bias voltage Vbias is at the lower bound. In response, thebias controller 330 may send a control signal at the output terminal MX1to the multiplexer 340 that switches input 342 from being connected tothe first output 344 to being connected to the second output 346. Inturn, when the input 342 is connected to the second output 346, currentmay flow through the diode D2 and the switch M3 to node B, and the biasvoltage Vbias may increase. The bias voltage Vbias may increase to theupper bound of the target range in several switching cycles. The biascontroller 330 may sense at the input terminal SNS1 that the biasvoltage Vbias is at the upper bound. In response, the bias controller330 may send a control signal at the output terminal MX1 to themultiplexer 340 that switches the input 342 from being connected to thesecond output 346 to the first output 344. In turn, when the input 342is connected to the first output 344, no current may flow through thediode D2 and the switch M3, and the bias voltage Vbias may decrease.

The bias controller 330 may continually operate to sense the biasvoltage Vbias at node B and send a control signal to the multiplexer 340to maintain the bias voltage Vbias within a target range and/or fromexceeding an upper bound of the target range or falling below a lowerbound of the target range. In this way, the bias circuit 320 may beconfigured to supply a bias signal to power the control circuit 310 in aby hysteretic manner. When the bias voltage Vbias increases to an upperbound of a target range, the bias controller 330 may configure themultiplexer 340 so that the control circuit 310 is switching the switchM1 “on” and “off” in order to decrease the bias voltage Vbias. Also,when the bias voltage Vbias decreases to a lower bound of a targetrange, the bias controller 330 may configure the multiplexer 340 so thatthe control circuit 310 is switching the switch M3 “on” and “off” inorder to increase the bias voltage Vbias.

The multiplexer 340 may be configured to shift the level of the signalfrom GD1 when it passes that signal to the second output 346 so that thethird switch M3 receives the appropriate gate voltage level to turn “on”or “off.”

Additionally, like the bias circuit 120 shown in FIG. 1, the biascircuit 320 may be configured to control the bias voltage Vbias appliedto the control circuit 310 independent of the switching signals outputfrom GD1. Rather than monitor the switching signal output from GD1and/or an output Vout of the switched-mode power supply 300 anddetermine whether to send switching signals to either the switch M1 orthe switch M3 based on the output from GD1 and/or the output Vout of theswitch-mode power supply 100, the bias controller 130 may monitor thebias voltage Vbias itself, and determine whether to send switchingsignals to either the switch M1 or the switch M3 based on the level ofthe bias voltage Vbias.

FIG. 4 shows a schematic diagram of an example switch-mode power supply400, illustrating an example cascode configuration of the switch-modepower supply 300. In the example switch-mode power supply 400, a firstswitch M1 may be connected to a switch M2 in a cascode configuration.The switch-mode power supply 400 may further include a multiplexer 440that is configured to receive a switching signal output from a controlcircuit 410 at an input 442. The multiplexer 440 may be configured tocommunicate the switching signal to either the first switch M1 via afirst output 444 or to an input TRG of a bias controller 430 via asecond output 446.

In operation, when the multiplexer 440 communicates the switching signalto the first switch M1, the first switch M1 may switch “on” and “off”and the second switch M2 may be in an “off” state. As a result, nocurrent may flow through a diode D2 to node B and the voltage bias Vbiasbeing applied to the voltage bias input terminal Vcc may decrease ascharge stored in the energy storing circuit C2 is discharged into theload Z2. Alternatively, when the multiplexer 440 communicates theswitching signal to the input terminal TRG of the bias controller 430,the input terminal TRG may communicate the switching signal to an outputterminal GD2 that communicates the switching signal to an input (e.g., agate) of the second switch M3. When communicating the switching signalfrom the input terminal TRG to the output terminal GD2, the biascontroller 430 may be configured to perform any level shifting that isnecessary. The level shifting is necessary to raise the gate voltage ofM2 substantially above node B or node A voltage to turn on M2. Also,when the multiplexer 440 is communicating the switching signal to theinput terminal TRG, the first switch M1 may be maintained in the “off”state. When the second switch M2 is “on” and the first switch M1 is“off,” current output from the inductor L1 may flow through the secondswitch M2, through the diode D2 of the bias circuit 420, and to node B.As a result, the voltage at node B (Vbias) may increase.

During startup, the current through the resistor R1 may charge thecapacitor C3 from zero volts to a predetermined voltage that may startthe operation of the control circuit 410. The bias controller 430 maysense the voltage at node B through the terminal SNS1. The biascontroller 430 may also use the voltage at node B to power itself and/orto generate the switching signal at the output terminal GD2. The biascontroller 430 may hold the terminals SNS1 and GD2 at the same level soas to facilitate the second switch M2 being turned “on” or “off” when M1is turned “on” or “off.”

The bias controller 430 may be configured to sense the voltage biasVbias. The bias controller 430 may also be configured to determinewhether the voltage bias Vbias is at an upper bound or a lower bound ofa target range. If the voltage bias is at the upper bound, then the biascontroller 430 may be configured to output a control signal at an outputterminal MX1 that configures the multiplexer 440 to communicate theswitching signal to the first switch M1 in order to reduce the voltagebias Vbias. Alternatively, if the voltage bias is at the lower bound,then the bias controller 430 may be configured to output a controlsignal at the output terminal MX1 that configures the multiplexer 440 tocommunicate the switching signal to the input terminal TRG of the biascontroller 430 in order to increase the voltage bias Vbias.

FIG. 5 shows a schematic diagram of an example switch-mode power supply500, illustrating another example cascode configuration of theswitch-mode power supply 300. In the example switch-mode power supply500, a first switch M1 may be connected to a switch M2 in a cascodeconfiguration. The switch-mode power supply 500 may further include amultiplexer 540 that is configured to receive a switching signal outputfrom a control circuit 510 at an input 542. The multiplexer 540 may beconfigured to communicate the switching signal to either the firstswitch M1 via a first output 544 or to an input terminal TRG of a biascontroller 530 via a second output 546. When the input terminal TRGreceives the switching signal, the switching signal may be communicatedto an output terminal GD2. The output terminal GD2 may communicate theswitching signal to an input (e.g., a gate) of a switch M3 of the biascircuit 530.

Also, in the example switch-mode power supply 500, resistor R2 may beconnected from the power source Vin to the gate terminal of M2. Acapacitor C3 and a zener diode may also connect from the gate of M2 toground.

In operation, when the multiplexer 540 communicates the switching signalto the first switch M1, the first switch M1 may switch “on” and “off.”When the multiplexer 540 communicates the switching signal to the firstswitch M1, the switching signal is not being applied to the switch M3.As a result, no current or substantially no current may flow from node Athrough the diode D2 and the switch M3 to node B, and the bias voltageVbias may decrease. As the first switch M1 turns “on” and “off,” thesecond switch M2 turns “on” and “off.” When both the first switch M1 andthe second switch M2 are “on,” the current in the inductor L1 may flowto ground. Alternatively, when the first switch M1 and the second switchM2 are both “off,” the current in the inductor L1 flows through D1 tothe output of the example switch-mode power supply 500.

Alternatively, when the multiplexer 540 communicates the switchingsignal to the input terminal TRG, the switching signal may be output tothe switch M3 at the output terminal GD2. Also, when the multiplexer 540communicates the switching signal to the input terminal TRG, the firstswitch M1 may not receive the switching signal and may be maintained inthe “off” state, which may forward bias the diode D2, turning the diodeD2 “on.” When the switching signal turns the switch M3 “on,” the secondswitch M2 may also be configured to turn “on.”0 As a result, currentbeing output from the inductor L1 may flow through the second switch M2,through the diode D2 and the switch M3 to node B, and the bias voltageVbias may increase. Alternatively, when the switching signal turns theswitch M3 “off,” the second switch M2 may also be configured to turn“off.” As a result, current being output from the inductor L1 may passthrough the diode D1 to the output of the switch-mode power supply 500.

The bias controller 530 may be configured to sense the voltage biasVbias. The bias controller 530 may also be configured to determinewhether the voltage bias Vbias is at an upper bound or a lower bound ofa target range. If the voltage bias is at the upper bound, then the biascontroller 530 may be configured to output a control signal at an outputterminal MX1 that configures the multiplexer 540 to communicate theswitching signal to the first switch M1 in order to reduce the voltagebias Vbias. Alternatively, if the voltage bias is at the lower bound,then the bias controller 530 may be configured to output a controlsignal at the output terminal MX1 that configures the multiplexer 540 tocommunicate the switching signal to the input terminal TRG of the biascontroller 530 in order to increase the voltage bias Vbias.

FIG. 6 shows a schematic diagram of an alternative example switch-modepower supply 600. In the example switch-mode power supply 600, a switchM3 may be connected in series at node A with an output of the exampleswitch-mode power supply 300, which may include a parallel combinationof an output capacitor C1 and an output load Z1. The switch M3 may beconnected to the parallel combination so that the output voltage Voutwith reference to ground is the voltage across the parallel combinationof the output capacitor C1 and the output load Z1 in addition to thevoltage across the switch M3 (e.g., the drain-source voltage). A diodeD2 of a bias circuit 620 may be connected to the parallel combinationand the switch M3 at node A. The diode D2 may also be connected to avoltage bias input terminal Vcc of a control circuit 610 at node B. Thecontrol circuit 610 may also include an output terminal GD1 that isconfigured to output switching signals to a switch M1 that switches theswitch M1 “on” and “off.”

In operation, the control circuit 610 may output switching signals atthe output terminal GD1 to a switch M1 to turn the switch M1 “on” and“off.” When the switch M1 is “on,” current discharged from an inductorL1 may pass through the switch M1 to ground. Alternatively, when theswitch M1 is “off,” current discharged from the inductor L1 may passthrough the diode D1 to the output of the switch-mode power supply 300.In turn, the current may pass through the output load Z1 to node A. Whenthe switch M3 is “on,” current flowing through the output load Z1 tonode A may pass through the switch M3 to ground. Also, when the switchM3 is “on,” the switch M3 may have a voltage drop of approximately zerovolts, causing the switch M3 to act as a short circuit from node A toground. As such, when the switch M3 is “on,” the diode D2 may be reversebiased and no current, or substantially no current, may flow from node Athrough the diode D2, to node B. Alternatively, when switch M3 is “off,”the diode D2 may be forward biased, and current flowing through theoutput load Z1 to node A may pass through the diode D2 to node B.

As current passes through the diode D2 to node B, charge may be storedin the energy storing circuit C2, generating a bias voltage Vbias thatis applied to the voltage bias input terminal Vcc to power the controlcircuit 610. As previously described, the bias voltage Vbias mayincrease as the charge is continually stored in the energy storingcircuit C2. An input terminal SNS1 of the bias controller 630 may beconfigured to sense the bias voltage Vbias. In the example switch-modepower supply 600, the bias controller 630 may be configured to controlswitching of the switch M3. In particular, the bias controller 630 maybe configured to output switching signals at an output GD2 to an inputterminal (e.g., a gate) of the switch M3 to turn the switch M3 “on” and“off.”

The bias controller 630 may be configured to turn the switch M3 “on” fora first period of time and turn the switch M3 “off” for a second periodof time. The first period of time may be the same as or different fromthe second period of time. Also, the first period of time and/or thesecond period of time may be determined independent of a switchingfrequency or period of the switching signals sent from the controlcircuit 610 to the switch M1. In some example configurations, the firstperiod of time and/or the second period of time may be longer induration than the time period of die switching signals output from thecontrol circuit 610. In other example configurations, the first periodof time and/or the second period of time may be equal to or less thanthe time period of the switching signals output from the control circuit610.

The first period of time and/or the second period of time may bedependent upon a target range associated with the bias voltage Vbias.The target range may include and/or be centered around a target level.The target range may have an upper bound and a lower bound. When theswitch M3 is turned “on,” the bias voltage Vbias at node B may decreasebecause no current or substantially no current may flow through thediode D2, and charge stored in the energy storing circuit C2 may bedischarged into the load Z2 and/or the voltage bias input terminal Vcc.The bias controller 630 may sense the bias voltage Vbias at the inputterminal SNS1. When the bias voltage Vbias decreases to the lower boundof the target range, the bias controller 630 may be configured to outputa switching signal from the output terminal GD2 to the switch M3 thatturns the switch M3 from “on” to “off.” Alternatively, the biascontroller 630 may be configured to cease outputting the switchingsignal. When the switch M3 is turned “off,” the bias voltage Vbias atnode B may increase as current may flows through diode D2 to node B. Theswitch M3 may be maintained in the “off” state, and while the switch M3is “off,” the bias voltage Vbias may increase as current passes throughthe diode D2 and charge is stored in the energy storing circuit C2. Thebias controller 630 may sense the increasing bias voltage Vbias at theinput terminal SNS1. When the bias voltage Vbias increases to the upperbound of the target range, the bias controller 630 may be configured tooutput a signal from the output terminal GD2 that turns the switch M3from “off” to “on.” As previously described, when the switch M3 isturned “on,” current passing through the output load Z1 to node A maynot pass through the diode D2 to node B, and the bias voltage Vbias atnode B may decrease.

The bias controller 630 may continually operate to sense the biasvoltage Vbias at node B and send a control signal to the switch M3 tomaintain the bias voltage Vbias within a target range and/or fromexceeding an upper bound of the target range or falling below a lowerbound of the target range. In this way, the bias circuit 620 may beconfigured to supply a bias signal to power the control circuit 610 in ahysteretic manner. When the bias voltage Vbias increases to an upperbound of a target range, the bias controller 630 may control the switchM3 to increase or decrease the bias voltage Vbias, depending on whetherthe bias voltage Vbias is at the upper bound or the lower bound.

Additionally, like the bias circuits 120 and 320 shown in FIGS. 1 and 3,the bias circuit 620 may be configured to control the bias voltage Vbiasapplied to the control circuit 310 independent of the switching signalsoutput from GD1. Rather than monitor the switching signal output fromGD1 and/or an output Vout of the switched-mode power supply 600 anddetermine whether to the switch M3 “on” or “off” based on the outputfrom GD1 and/or the output Vout of the switch-mode power supply 600, thebias controller 630 may monitor the bias voltage Vbias itself anddetermine whether to the switch M3 “on” or “off” based on the level ofthe bias voltage Vbias.

FIG. 6 shows the switch M3 as a component of the example switch-modepower supply 600 that is external to the bias circuit 620. In otherexample configurations, the switch M3 may be a component of the biascircuit 620, similar to the switch M3 being a component of the biascircuit 120 shown in FIG. 1 and the bias circuit 320 shown in FIG. 3.

One or more of the control circuits 110, 210, 310, 410, 510,610, thebias circuits 120, 220, 320, 410, 520,620, and/or the bras controllers130,230, 330, 430, 530,630 shown in FIGS. 1-6 may be and/or may includea portion or all of one or more processing systems of various kinds,such as the processing system 700 in FIG. 7. In some examples, theprocessing system 700 may include a processor and memory. The processingsystem 700 may include a set of instructions that can be executed tocause the processing system 700 to perform any one or more of themethods or computer based functions disclosed.

In FIG. 7, the example processing system 700 may include a processor702, e.g., a central processing unit (CPU), a graphics processing unit(GPU), or both. The processor 702 may be one or more general processors,digital signal processors, application specific integrated circuits,field programmable gate arrays, servers, networks, digital circuits,analog circuits, combinations thereof, or other now known or laterdeveloped devices for analyzing and processing data. The processor 702may implement a software program, such as code generated manually (i.e.,programmed).

The term “module” may be defined to include a plurality of executablemodules. As described herein, the modules are defined to includesoftware, hardware or some combination thereof executable by aprocessor, such as processor 702. Software modules may includeinstructions stored in memory, such as memory 704, or another memorydevice, that are executable by the processor 702 or other processor.Hardware modules may include various devices, components, circuits,gates, circuit boards, and the like that are executable, directed,and/or controlled for performance by the processor 702.

The processing system 700 may include a memory 704, such as a memory 704that can communicate via a bus 708. The memory 704 may be a main memory,a static memory, or a dynamic memory. The memory 704 may include, but isnot limited to computer readable storage media such as various types ofvolatile and non-volatile storage media, including but not limited torandom access memory, read-only memory, programmable read-only memory,electrically programmable read-only memory, electrically erasableread-only memory, flash memory, magnetic tape or disk, optical media andthe like. In one example, the memory 704 includes a cache or randomaccess memory for the processor 702. In alternative examples, the memory704 is separate from the processor 702, such as a cache memory of aprocessor, the system memory, or other memory. The memory 704 may be anexternal storage device or database for storing data. Examples include ahard drive, compact disc (“CD”), digital video disc (“DVD”), memorycard, memory stick, floppy disc, universal serial bus (“USB”) memorydevice, or any other device operative to store data. The memory 704 isoperable to store instructions executable by the processor 402. Thefunctions, acts or tasks illustrated in the figures or described may beperformed by the programmed processor 702 executing the instructionsstored in the memory 704. The functions, acts or tasks are independentof the particular type of instructions set, storage media, processor orprocessing strategy and may be performed by software, hardware,integrated circuits, firm-ware, micro-code and the like, operating aloneor in combination. Likewise, processing strategies may includemultiprocessing, multitasking, parallel processing and the like.

The present disclosure contemplates a computer-readable medium 722 inwhich one or more sets of instructions 724, e.g. software, can beembedded. Further, the instructions 724 may embody one or more of themethods or logic as described. In a particular example, the instructions724 may reside completely, or at least partially, within the memory 704and/or within the processor 702 during execution by the processingsystem 700. The memory 704 and the processor 702 also may includecomputer-readable media as discussed above. While the computer-readablemedium is shown to be a single medium, the term “computer-readablemedium” may include a single medium or multiple media, such as acentralized or distributed database, and/or associated caches andservers that store one or more sets of instructions. The term“computer-readable medium” may also include any medium that is capableof storing, encoding or carrying a set of instructions for execution bya processor or that cause a computer system to perform any one or moreof the methods or operations disclosed. The “computer-readable medium”may be non-transitory, and may be tangible.

In an example, the computer-readable medium can include a solid-statememory such as a memory card or other package that houses one or morenon-volatile read-only memories. Further, the computer-readable mediumcan be a random access memory or other volatile rewritable memory.Additionally, the computer-readable medium can include a magneto-opticalor optical medium, such as a disk or tapes or other storage device tocapture carrier wave signals such as a signal communicated over atransmission medium. A digital file attachment to an e-mail or otherself-contained information archive or set of archives may be considereda distribution medium that is a tangible storage medium. Accordingly,the disclosure is considered to include any one or more of acomputer-readable medium or a distribution medium and other equivalentsand successor media, in which data or instructions may be stored.

In an alternative example, dedicated hardware implementations, such asapplication specific integrated circuits, programmable logic arrays andother hardware devices, can be constructed to implement various parts ofthe switch-mode power supplies. Applications that may include theapparatus and systems can broadly include a variety of electronic andcomputer systems. One or more examples described may implement functionsusing two or more specific interconnected hardware modules or deviceswith related control and data signals that can be communicated betweenand through the parts of the switch-mode power supplies, or as portionsof an application-specific integrated circuit. The present systemencompasses software, firmware, and hardware implementations.

FIG. 8 shows a flow diagram of an example method 800 of operating, apower supply to maintain an auxiliary bias being applied to a controlcircuit of the power supply within a target range. At block 802, a biassignal may be output from a bias circuit of the power supply. The biassignal may be used to generate the auxiliary bias. At block 804, thebias circuit and/or a bias controller of the bias circuit, may determineand/or sense a level of the auxiliary bias being applied to the controlcircuit. At block 806, the bias circuit and/or the bias controller ofthe bias circuit, may determine whether the level is with a targetrange. If the level is within the target range, then the method mayproceed back to block 802, where bias circuit continues outputting thebias signal.

Alternatively, if the auxiliary bias is not within the target range,then the method may proceed to block 808, where the bias circuit and/orthe bias controller may change a switching signal being applied to aswitch that outputs the bias signal. By changing the switching signal,the bias signal being output may change, which increases or decreasesthe auxiliary bias. As previously described, a dc level of the switchingsignal may be changed to a level that meets or exceeds a threshold levelthat turns the switch “on” in order to increase the auxiliary bias; orthe dc level may be changed to a level that is below a threshold levelthat turns the switch “off” in order to decrease the auxiliary bias.Alternatively, a duty cycle of the switching signal may be increased toincrease an amount of time that the switch is “on” in order to increasethe auxiliary bias; or the duty cycle may be decreased to decrease anamount of time that the switch is “on-” in order to decrease theauxiliary bias. Also at block 808, the changed switching signal may beapplied to the switch to change the bias signal, and in turn theauxiliary bias. The method may proceed back to block 804, where the biascontroller senses the auxiliary bias.

FIG. 9 shows a flow diagram of an alternative example method 900 ofoperating a power supply to maintain an auxiliary bias being applied toa control circuit of the power supply within a target range. At block902 a switching signal is output from a control circuit to amultiplexer, and the multiplexer may communicate the switching signal toeither a first switch or a second switch. The second switch may output abias signal that is used to generate an auxiliary bias used to power thecontrol circuit. At block 904, a bias controller may determine and/orsense the auxiliary bias. At block 906, the bias controller maydetermine whether the auxiliary bias is at an upper bound or a lowerbound of a target range. If the auxiliary bias is not at the upper boundor the lower bound, then the method may proceed back to block 902, wherethe multiplexer continues and/or maintains communicating the switchingsignal to the same switch that the multiplexer has been communicatingthe switching signal to. Alternatively, if the auxiliary bias is at theupper bound or the lower bound of the target range, then at block 908,the multiplexer may output the switching signal to the other of switch.By switching communication of the switching signal to the other switch,the auxiliary bias may be maintained within the target range. Afterswitching communication of the switching signal to the other switch, themethod may proceed back to block 904, where the auxiliary bias issensed.

FIG. 10 shows a flow diagram of an alternative example method 1000 ofoperating a power supply to maintain an auxiliary bias being applied toa control circuit of the power supply within a target range. At block1002, a switching signal may be applied to a switch that turns theswitch “on” or “off.” At block 1004, a level of the auxiliary bias maybe sensed by the bias circuit. At block 1006, the bias circuit maydetermine whether the auxiliary bias is at an upper bound or a lowerbound of a target range. If the auxiliary bias is not at the upper boundor the lower bound, then the method may proceed back to block 1002,where the switch is maintained in the “on” state or the “off” state.Alternatively, if the auxiliary bias is at the upper bound or the lowerbound, then the method may proceed to block 1008, where the switch isturned to the other state. For example, if the switch is “on,” then theswitch may be turned to being “off.” Alternatively, if the switch is“off,” then the switch may be turned to being “on.” After turning theswitch to the other state, the method may proceed back to block 1004,where the auxiliary bias is sensed.

Various embodiments described herein can be used alone or in combinationwith one another. The foregoing detailed description has described onlya few of the many possible implementations of the present invention. Forthis reason, this detailed description is intended by way ofillustration, and not by way of limitation.

I claim:
 1. A power supply comprising: a switch; a first circuit that isconfigured output a switching signal to control switching of the switch;and a second circuit that is configured to generate a bias signal thatis used to power the first circuit, the bias signal being generatedindependent of the switching signal output from the first circuit
 2. Thepower supply of claim 1, wherein the second circuit is furtherconfigured to: sense a bias voltage being applied to the first circuitto power the first circuit; and change the bias signal being output fromthe second circuit in order to adjust the bias voltage being applied tothe first circuit, the change being based on a comparison of the biasvoltage and a predetermined value.
 3. The power supply of claim 2,wherein the predetermined is one of an upper bound and a lower bound ofa target range.
 4. The power supply of claim 2, wherein the switchcomprises a first switch, and wherein the second circuit comprises: asecond switch configured to output the bias signal; and a controller incommunication with the switch, wherein the controller is configured tocontrol switching of the second switch to change the bias signal beingoutput from the second switch.
 5. The power supply of claim 4, whereinthe controller is configured to change a duty cycle of a switchingsignal being applied to the second switch to change the bias signal. 6.The power supply of claim 4, wherein the controller is configured toturn the second switch “on” to increase the bias voltage being appliedto the first circuit, and to turn the second switch “off” to decreasethe bias voltage being applied to the first circuit.
 7. The power supplyof claim 4, wherein the bias circuit further comprises: a diodeconnected to the second switch, wherein the diode is configured to turn“on” when the first switch turns “off,” and wherein the bias signal isoutput from the bias circuit when the diode and the second switch are“on.”
 8. The power supply of claim 2, wherein the switch comprises afirst switch, wherein the second circuit comprises a second switchconfigured to output the bias signal and wherein the switch-mode powersupply further comprises: a multiplexer alternatingly in communicationwith the first switch and the second switch, the multiplexer configuredto receive the switching signal from the first circuit; andalternatingly communicate the switching signal to the first switch andthe second switch, wherein the second circuit is configured to changethe bias signal when the multiplexer switches communicating theswitching signal from one of the first switch and the second switch tothe other of the first switch and the second switch.
 9. The power supplyof claim 8, wherein the first switch is configured to be in an “off”state and the second switch is configured to output the bias signal toincrease the bias voltage when the multiplexer communicates theswitching signal to the second switch, and wherein the second switch isconfigured to be in an “off” state and the first switch is configured todraw current to decrease the bias voltage when the multiplexercommunicates the switching signal to the first switch.
 10. The powersupply of claim 8, wherein the second circuit comprises: a controllerthat is configured to: configure the multiplexer to communicate theswitching signal to the first switch when the bias voltage is at anupper bound of a target range; and configure the multiplexer tocommunicate the switching signal to the second switch when the biasvoltage is at a lower bound of a target range.
 11. The power supply ofclaim 2, wherein the switch comprises a first switch, and wherein thepower supply further comprises a second switch connected in series withan output load, wherein the second circuit comprises: a diode configuredto output the bias signal; and a controller configured to controlswitching of the second switch, wherein the controller is configured toturn the second switch “on” to draw current through the second switch sothat the diode is “off” and the bias voltage decreases, and wherein thecontroller is configured to turn the second switch “off” to turn thediode “on” so that the diode outputs the bias signal to increase thebias voltage.
 12. The power supply of claim 11, wherein the controlleris configured to: turn the second switch “on” when the bias voltage isat an upper bound of a target range; and turn the second switch “off”when the bias voltage is at a lower bound of a target range.
 13. Thepower supply of claim 2, wherein the switch comprises a first switch,the power supply further comprising a second switch connected to thefirst switch in a cascode configuration, wherein the second circuit isconfigured to: receive current from the second switch; and change thebias signal by outputting at least some of the current received from thesecond switch.
 14. A method of maintaining an auxiliary bias of a powersupply within a target range, the method comprising: outputting, with abias circuit, a bias signal that generates the auxiliary bias, theauxiliary bias powering a control circuit that controls switching of aswitch of the power supply; sensing, with the bias circuit, theauxiliary bias; in response to sensing the auxiliary bias, changing,with the bias circuit, the bias signal being output from the biascircuit to adjust the auxiliary bias.
 15. The method of claim 14,wherein the switch comprises a first switch, the method furthercomprising: in response to sensing the auxiliary bias, changing, with acontroller of the bias circuit, a switching signal applied to a secondswitch to change the bias signal.
 16. The method of claim 15, whereinchanging the switching signal applied to the second switch to change thebias signal comprises: increasing, with the controller of the biascircuit, a duty cycle of the switching signal to increase an amount ofthe bias signal being output from the bias circuit; and decreasing, withthe controller of the bias circuit; the duty cycle of the switchingsignal to decrease an amount of the bias signal being output from thebias circuit.
 17. The method of claim 14, wherein the switch comprises afirst switch, the method further comprising: receiving, with amultiplexer, a switching signal from the control circuit; in response tosensing the auxiliary bias, outputting, with the controller of the biascircuit, a control signal to the multiplexer that configures themultiplexer to output the received switching signal to one of the firstswitch and a second switch to change the bias signal, the second switchoutputting the bias signal.
 18. The method of claim 17, wherein inresponse to sensing that the auxiliary bias is at an upper bound of atarget range, outputting, with the controller of the bias circuit, afirst control signal that configures the multiplexer to communicate theswitching signal to the first switch, and wherein in response to sensingthat the auxiliary bias is at a lower bound of a target range,outputting, with the controller of the bias circuit, a second controlsignal that configures the multiplexer to communicate the switchingsignal to the second switch.
 19. The method of claim 14, wherein theswitch comprises a first switch, the method further comprising:switching a second switch to an “on” state to decrease the auxiliarybias, the second switch being connected in series with an output load;and switching the second switch to an “off” state to increase theauxiliary bias.
 20. The method of claim 19, wherein the second switch isswitched to the “on” state in response to sensing that the auxiliarybias is at a lower bound of a target range, and wherein the secondswitch is switched to the “off” state in response to sensing that theauxiliary bias is at an upper bound of the target range.
 21. A lightingsystem comprising: a power supply comprising: a switch; a first circuitthat is configured output a switching signal to control switching of theswitch; and a second circuit comprising a feedback loop that isconfigured to output a bias signal that is used to generate an auxiliarybias that power the first circuit, sense the auxiliary bias; change thebias signal to adjust a level of the auxiliary in response to the sensedauxiliary bias; a light source comprising at least one light-emittingdiode connected to an output of the power supply.
 22. The lightingsystem of claim 21, wherein the switch comprises a first switch, andwherein the second circuit comprises; a second switch configured tooutput the bias signal; and a controller in communication with theswitch, wherein the controller is configured to control switching of thesecond switch to change the bias signal being output from the secondswitch.
 23. The lighting system of claim 21, wherein the switchcomprises a first switch wherein the second circuit comprises a secondswitch configured to output the bias signal, and wherein the switch-modepower supply further comprises: a multiplexer alternatingly incommunication with the first switch and the second switch, themultiplexer configured to receive the switching signal from the firstcircuit, and alternatingly communicate the switching signal to the firstswitch and the second switch, wherein the second circuit is configuredto change the bias signal when the multiplexer switches communicatingthe switching signal from one of the first switch and the second switchto the other of the first switch and the second switch.
 24. The lightingsystem of claim 21, wherein the switch comprises a first switch, andwherein the power supply further comprises a second switch connected inseries with an output load, wherein the second circuit comprises: adiode configured to output the bias signal; and a controller configuredto control switching of the second switch, wherein the controller isconfigured to turn the second switch “on” to draw current through thesecond switch so that the diode is “off” and the bias voltage decreases,and wherein the controller is configured to turn the second switch “off”to turn the diode “on” so that the diode outputs the bias signal toincrease the bias voltage.